1. Field of the Invention
This invention relates to a differential controlling device for a differential gear and, more particularly, to a device for controlling the rotational speed differential, which is generated to shafts respectively connected to a pair of side gears in cooperation with a differential case, a plurality of pinions and the pair of side gears respectively disposed in the differential case, in a differential gear capable of being limited by limiting means.
2. Description of the Prior Art
Various devices for controlling the rotational speed differential of output shafts of a differential gear have been proposed.
The Japanese Patent Publication No. 40454/80 has disclosed a differential controlling device, in which a clutch member is swung by pedalling a brake pedal to press a side gear against a differential case for limiting the rotational speed differential.
The Japanese Utility Model Public Disclosure (KOKAI) No. 150630/84 has disclosed a differential controlling device for a vehicle, in which after a steering angle of the vehicle is detected and a detected value is conducted to a comparator, a control circuit is operated to limit the rotational differential according to the steering angle.
The Japanese Utility Model Public Disclosure (KOKAI) No. 158745/84 has disclosed a differential gear with a differential lock, in which, the differential lock is released to permit a rotational speed differential when vehicle speed exceeds a predetermined value.
Either of types of the devices noted above cannot solve any problem caused by braking when left and right wheels travel on road surfaces having different coefficients of friction, i.e., a so called frictionally different road.
When the rotational speed differential is controlled during the braking of the vehicle travelling on the frictionally different road to obviate the rotational difference between left and right wheels at the time of straight travelling and braking, the slip ratios of left and right wheels are equalized with each other to make a difference in braking forces. Thus, since the vehicle deviates to effect an unstable behavior, it is not preferable to limit the rotational speed differential when braking during in straight advance travelling on the frictionally different road. On the other hand, in case when turning the vehicle on the frictionally different road, swinging of a rear vehicle portion due to early wheel resulting from lead shifting lock of an inside wheel and an unstable behavior due to the reduction of braking forces are more unfavorable than the deviation of the vehicle due to the difference in the braking forces. Therefore, it is more preferable to limit the differential in this case.